Combining the Environmental Protection Agency?s Air Toxics in Ambient Air data with US Census data, this project will develop a measure of inequality of exposure between non-Hispanic African Americans and non-Hispanic Whites. This is the Net Difference Score, which is the probability that a randomly selected Black person has a higher exposure than a randomly selected White person minus the probably that the White person has a higher exposure than the Black person. Using data available on the census tract level, the Net Difference score will be calculated for the 50 metropolitan areas over 1,000,000 in population. This inequality measure is based on peer-reviewed techniques developed for economics and social science analysis. It will be compared to more traditional measures of inequality, i.e., differences in mean exposure. Secondly, this project will attempt to identify some of the factors associated with differences in disparities across these metropolitan areas. Preliminary research shows that there is a wide variation in exposure disparities. To understand these differences, an analysis using income inequality, racial segregation, proportion of work force in manufacturing industries and other data will be used to begin to try to explain why some areas have greater disparities than others. The analysis will have to control for certain other potential factors such as Black-White differences in income in order to better identify these impacts. Measures for income inequality, racial segregation and other factors will be adapted from peer-reviewed research in economics and social sciences. All data will be derived or directly imported from publicly available data sources.